Gas analysis,a method of and a gas analyzer for accomplishing same

ABSTRACT

A METHOD AND A FACILITY FOR MEASURING GAS COMPOSITION BASED ON THE MEASUREMENT OF TIME REQUIRED TO HEAT A SORBENT INTRODUCED INTO THE GAS MIXTURE TO BE ANALYZED UP TO A SPECIFIED TEMPERATURE AT WHICH INTENSIVE DESORPTION OF THE MIXTURE COMPONENT SORBED BY THE SORBENT TAKES PLACE. THE SORBENT COATS THE THERMISTOR INCORPORATED INTO AN ARM OF A MEASURING BRIDGE WHOSE SUPPLY CIRCUIT INCLUDES A KEY AND THE MEASURING DIAGONAL INCLUDES A BALANCE DETECTOR. THE THERMISTOR HEATING TIME IS MEASURED BETWEEN THE MOMENT OF POWER SUPPLY TO THE BRIDGE AND OF THE SIGNAL RECEPTION FROM THE BALANCE DETECTOR. THE MODIFICATIONS OF THE FACILITY INCLUDE DIFFERENTIAL CONNECTION OF TWO THERMISTORS COATED WITH DIFFERENT SORBENTS, AND STABILIZATION OF THE INITIAL TEMPERATURE OF THE THERMISTORS.

Oct. 5, 197i D. l. AGEIKIN ETAL 3,610,023

GAS ANALYSIS A METHOD OF AND A GAS ANALYZER FOR ACCOMPLISHING SAMEAldaar/.1 fr a..

Oct. 5, 1971 D, l, AGElKlN ETAL 3,610,023

GAS ANALYSIS A METHOD OF AND A GAS ANALYZER FOR ACCOMPLISHING SAME FiledNOV. 14, 1969 5 Sheets-Sheet 2 THEEM/s To/Es luce dEECTOES F/E. Z

@wlww Oct. 5, 1971 D -L AGElKlN ETAL 3,610,023

GAS ANALYSIS A METHOD OF AND A GAS ANALYZER FOR ACCOMPLISHING SAME 5Sheets-Shoot l Filed Nov. 14. 1969 Arraamrr United States Patent O3,610,023 GAS ANALYSIS, A METHOD OF AND A GAS ANALYZER FOR ACCOMPLISHINGSAME Dmitry Ivanovich Ageikin, Belyaevo-Bogorodskoe, kvartal 46-47,korpus 48, kv. 63; Ekaterina Nikolaevna Kostina, Leninsky prospekt 101,korpus 135, 65; Vadim Fedorovich Zhuravlev, Lazarevksyay ulitsa 4, kv.1; Jury Tovievich Knopov, Olouetskaya ulitsa 38a; and VladimirVasilievich Dorofeev, Leninsky prospekt 81, kv. 56, all of Moscow,U.S.S.R.; and Alexei Nikolaevich Chernicliin, Ulitsa Popova 16, kv. 73;Igor Petrovich Mityashin, prospekt Gagarina 3, kv. 22; Arkady ShaevichKatsuelson, Ulitsa Kirova 26, kv. 17; and Alexandr Alexeevich `Golubev,Ulitsa Kozlova 5, kv. 18, all of Smolensk, U.S.S.R.

Filed Nov. 14, 1969, Ser. No. 876,957 Int. Cl. G01n 27/18 U.S. Cl. 73-276 Claims ABSTRACT OF THE DISCLOSURE A method and a facility formeasuring gas composition based on the measurement of time required toheat a sorbent introduced into the gas mixture to be analyzed up to aspeciiied temperature at which intensive desorption of the mixturecomponent sorbed by the sorbent takes place.

The sorbent coats the thermistor incorporated into an arm of a measuringbridge whose supply circuit includes a key and the measuring diagonalincludes a balance detector. The thermistor heating time is measuredbetween the moment of power supply to the bridge and of the signalreception from the balance detector. The modifications of the facilityinclude differential connection of two thermistor-s coated withdifferent sorbents, and stabilization of the initial temperature of thethermistors.

This invention relates to methods of gas analysis and to gas analyzersfor accomplishing same.

There are kno-wn chromatographic methods of gas analysis, which involvesorption of the gas being analyzed, followed by desorbing the gas bypassing a neutral gas through the sorbent bed, and determining thecomposition of the gas being analyzed from data on the content of itscomponents in the neutral gas directed to a detector. These knownmethods are useful for carry-ing out analyses of complex mixtures ofvarious gases.

However, the known methods are disadvantageous in that they cannot beaccomplished in a facile manner, as evidenced by the fact that gasanalyzers intended for embodying said methods are elaborate instrumentscomprising pumps, a gas cylinder, programmers, thermostats, andintricate detectors, so that the practical application or' said methodsis confined to cases where it is desired to effect an ultimate analysisof complex gas mixtures.

Another disadvantage of the known gas analysis methods consists in thatthe shape of output signals is inconvenient for feeding said signals toautomatic devices, and the chromatogram obtained should be subjected toanalysis and decoding.

Also known are gas analyzers, which incorporate at least one measuringbridge whose arms are formed by resistors and at least one thermistor,which contacts the gas being analyzed.

In the known gas analyzers, a thermistor heated by a current passedtherethrough experiences a heat loss and, consequently, a temperaturevariation depending upon the thermal conductivity of a sample gas, thepotential across the bridge diagonal being a gas analyzer output signal,which is proportional to the thermal conductivity of the sample gas.

The known gas analyzers are suitable for analyzing only simple binarygas mixtures, since the thermal conductivity of a complex mixturedepends upon the thermal conductivities of all mixture components.

Further disadvantages of the known gas analyzers are a relatively highpower consumption and the fact that the output signal (a low-leveldirect-current voltage) is inconvenient as a digital computer inputsignal.

Accordingly, it is an object of the present invention to provide a gasanalysis method, in particular a method for moisture concentrationmeasurements, which will be noted for a marked selectivity in analyzinga complex mixture of gases for a given component.

It is a further object of the present invention to provide a gasanalyzer for carrying out gas analyses by the method of the inventionwhich will make it possible, despite its relatively simple design, todetermine 'various components of gas mixtures and whose output signalwill be suitable as a digital compu-ter input signal.

It is the principal object of the invention to provide a method of gasanalysis, particularly a method for determining the content of moisture,which lends itself to realization by means of a gas analyzer having aunified standard design and a set of sensitive elements, 4whereinsuccessive incorporation of said elements into the measuring circuitwill make it possible to enhance the sensitiv-ity of gas mixturecomponent analyses.

This object is accomplished by the provision of a method of `gasanalysis, particularly a method of moisture content analysis, whichcomprises absorbing the gas being analyzed by sorbents, followed bydesorbing the gas in question wherein, according to the invention, gasdesorption is effected by heating at least one sorbent to pre-setthermal state characterizing the amount of the desorbed gas, e.g. to atemperature that corresponds to maximum desorption, the concentration ofthe absorbed gas mixture component being evaluated by measuring, in thecourse of sorbent heating, the time required to attain the aforesaidthermal state.

To realize said gas analysis method, in the gas analyzer, whichincorporates at least one measuring bridge, whose arms consist ofresistors and of at least one thermistor placed in the gas beinganalyzed, provision is made, according to the invention, for coating thethermistor with a sorbent that absorbs `the sought-for ygas mixturecornponent and for incorporating into the measuring diagonal of thebridge a balance detector that sends a signal once the thermistorattains the pre-set temperature, while the other diagonal of the bridgeincorporates a key intended to switch on power supply to the bridge andto a circuit that controls thermistor heating commencement.

The key may be made in the form of a balance detector-controlled controlelement of the thermistor temperature stabilizer, provision being madefor means of thermistor temperature setting.

It is further preferable that the key 4be furnished with a delayedself-actuating means.

It is further preferable that the means of thermistor temperaturesetting be made in the form of an auxiliary thermistor, which serves towarm up the sample gas surrounding the sorbent-coated thermistor andshould be switched into the measuring bridge in place of the saidsorbent-coated thermistor for a peiiod of time that precedes thecommencement of sample gas analysis.

It is also advantageous to provide in the circuit that controls thecommencement of thermistor heating at least one key in order to obtain asignal whose duration equals that of the thermistor heating period.

The abovementioned design features make the present gas analyzer simplein design, diminish power requirements, and provide for an output signalwhich can be readily digitalized, while the method of gas analysisrealized by the present gas analyzer makes for an enhanced selectivityof gas mixture analyses.

The present invention is illustrated hereinbelow by the description ofspecific embodiments thereof with reference to the accompanyingdrawings.

FIG. 1 represents the electrical circuit of the gas analyzer suggestedherein;

FIG. 2 represents the electrical circuit of the second modification ofthe same gas analyzer incorporating two measuring bridges;

FIG. 3 represents the electrical circuit'of the third modification ofthe gas analyzer described herein with a sorbent-coated thermistortemperature stabilizer.

FIG. 4 represents the electrical circuit of the fourth modification ofthe same gas analyzer with an auxiliar thermistor;

FIG. 5 represents the electrical circuit of the fifth modification ofthe gas analyzer described herein, including two measuring bridges andan auxiliary thermistor; and

'FIG. 6 represents the temperature variations versus time of asorbent-coated thermistor of the gas analyzer described herein accordingto FIG. 3.

The gas analyzer for gas mixture analyses, according to the presentinvention, includes power source 1 (FIG. 1), which energizes a measuringbridge, whose arms are formed by resistors 2-4 and thermistor 5, whichis contained in sample gas cell 6 and coated with sorbent 7, saidsorbent being capable of absorbing a gas mixture component beinganalyzed. Resistor 4 may be replaced with a thermistor selected so thatcurrent passage therethrough causes practically no heating thereof.

Incorporated in the measuring diagonal of the bridge is balance detector8, which sends a signal once thermistor 5 reaches a pre-set temperature.

The other diagonal of the bridge incorporates key 10 actuated byexternal control signal circuit 11 so that key 10 in the on positionsprovides for power supply from power source 1 to the measuring bridge.The interval meter 9 of any type is connected to the output of balancedetector 8 and the power source of the measuring bridge.

Where the thermal conductivity of the 'gas being analyzed varies withina wide range and said gas contains a component whose absorption by thesorbent introduces a significant error, use is made of a secondmodification of the gas analyzer, according to the invention, wherein,in contrast to the first modification, provision is made for twomeasuring bridges. In the second bridge, thermistor 12 (FIG. 2) andresistors 13, 3 and 4 are the bridge arms. Thermistor 12 is coated withsorbent 14, which is characterized by properties different from those ofsorbent 7, and placed in the gas being analyzed.

The measuring diagonal of the second bridge incorporates balancedetector 15, which transmits an appropriate signal once thermistor 14attains the pre-set temperature. Time interval meter 9 is connected tothe outputs of balance detectors 8 and 15 and to the power source of themeasuring bridges.

When the temperature of the gas being analyzed varies within a widerange, or Where it is desired to determine the content of a plurality ofcomponents in the gas mixture under test, said components beingessentially different from one another as to desorption temperatures, orelse in case the gas analyzer is to be readjusted for operation indifferent control ranges, in a third modification of the gas analyzer,according to the invention (FIG. 3), key 10 comprises a control elementof the temperature stabilizer of thermistor 5, said key being controlledby balance detector 8, while said temperature stabilizer serves as asensor of said control element. In the temperature stabilizer ofthermistor '5, provision is made for a means of setting the requisitetemperature of thermistor 5.

The measuring bridge arms consist of thermistor 5 and resistors 2, 4 and16-18, provision being made in key 10 for a delayed self-actuating means19, e.g. a single steady-state trigger.

In the gas analyzer modification under consideration,

in question are denoted in the drawing by reference numerals 25 and 26).

Coupled to the measuring bridge is integrating unit 27, which comprisesresistor 28 and capacitor 29, the output signal of said integrating unitover the intervals between measurements (in the absence of signals incircuits 25 and 26) being proportional to the temperature differencebetween thermistor S and the gas being analyzed.

The incorporation of integrating unit 27 into the gas analyzer circuitprovides the possibility of controlling continuously whether theanalyzer circuit is intact, as -well as of obtaining additional data onthe temperature of the gas being analyzed.

A fourth modification of the gas analyzer, according to the invention,differs from the third modification in that a means of setting thetemperature of thermistor 5 should, preferably, be made in the form ofauxiliary thermistor 30 (FIG. 4), which effects warming up the sampleIgas 1n the vicinity of thermistor 5. Thermistor 30 consists of awinding disposed around cell 6 lwhich is coupled to the measuring bridgein place of thermistor 5 for a period of' time preceding the actualanalysis of the sample gas, said Winding being connected together withthermistor 5 to key 31. Key 31 is coupled to the measuring bridge and 1sa component of external control signal circuit 32 (deslgnated in thedrawing by reference numeral 32), another component of said circuitbeing key 23, which 1s included, as pointed out hereinbefore, in thecircuit of tlme interval meter 9.

A fifth modification of the present gas analyzer, which may be regardedas a combination of the second and fourth modifications describedearlier, should preferably be used in instances where it is desired toattain a shorter response time of the gas analyzer, or where thetemperature and thermal conductivity of the gas being analyzed varywithin a wide range.

The essential distinctive featureof this .gas analyzer modification(FIG. 5) consists in that use is made of two measuring bridges whosearms are formed by thermistor 5 and resistors 2, 3 and 4, and thermistor12 and resistors 13, 3 and 4, respectively. Thermistor 12 is coated withsorbent 14, whose properties are distinct from the properties of sorbent7, said thermistor being placed in the sample gas.

A means of setting the temperature of thermistor 5 in the fifthmodification of the present gas analyzer consists of auxiliarythermistor 30, whose functions and location were described in detailearlier.

The first modification of the present gas analyzer (FIG. 1) operates onthe following principle.

In intervals between measurements, key 10 is in the off position, sothat the measuring bridge is deenergized. Sorbent 7 that coatsthermistor 5 contacts the gas being analyzed and absorbs therefrom acomponent of interest, e.g. moisture, in an amount that is proportionalto the partial pressure of said component.

To determine the concentration of the component, external controlcircuit 11 sends a control signal, which sets 'key 10 in the onposition, thereby energizing the measuring bridge from power source 1,so that there commences the heating of thermistor 5 and associateddescription of the gas mixture component previously absorbed by sorbent7. In so far as gas component desorption consumes heat, the process ofheating of thermistor slows down.

Once the thermistor 5 attains the pre-set temperature, which dependsupon the ratio of resistance offered by thermistor 5 and resistors 2, 3and 4, the potential across the measuring diagonal of the bridge dropsto a value, at which balance detector 8 is actuated. Key 10, whichswitches on the power supply circuit, simultaneously sends a signal thatthere commences the heating of thermistor 5, while balance detector 8sends a signal when the heating of thermistor 5 has been terminated. Thetime interval between said signals is measured by meter 9 to evaluatethe concentration of the gas component that has been absorbed by sorbent7.

The gas analyzer, therefore, embodies the gas analysis method, accordingto the invention, which comprises heating sorbent 7 until there isattained a pre-set thermal state consistent with the amount of thedesorbed gas, and measuring the time interval required for attainingsaid thermal state, the temperature at which balance detector 8 isactuated being the thermal state in question. The temperature isselected so that, once it is attained, the desorption of the previouslyabsorbed gas component will be at a maximum.

The second modication of the gas analyzer (FIG. 2) functions similarlyto the rst gas analyzer modification, except for the fact that in theinterval between two measurements there occurs the sorption of twocomponents from the gas mixture being analyzed or of combinations of gasmixture components by sorbents 7 and 14 applied onto two thermistors 5and 12. Once key 10 is set in the on position, there commences theheating of thermistor 12 simultaneously with thermistor 5, and onreaching the pre-set temperature by thermistor 12, said temperaturebeing governed by the ratio of the bridge arms constituted by resistors3, 4 and 13, and thermistor 12, balance detector 15 will be actuated byusing time interval meter 9 both the duration of each thermistor, 5 and12, heating and the difference of these durations can be measured. Inthe latter instance, the sensitivity of the method is essentiallyenhanced and the effect of variations in the thermal conductivity of thegas is compensated.

The third modication of the present gas analyzer (FIG. 3) functions asfollows. In intervals between measurements, keys 20, 21, 23, and 24 arein the off position, the ratio of the resistances of the measuringbridge arms formed by resistors 2, 16-18, and 4 and thermistor 5 beingsuch as to balance the bridge when the temperature of thermistor 5corresponds to the selected stabilization temperature which is somewhathigher than the temperature of the gas being analyzed. The operatingmode of the gas analyzer is set by the two-step temperature stabilizerof thermistor 5. When there occurs the heating of thermistor 5, whichserves as the sensitive element of thermistor 5, and heating proceedsuntil the stabilization temperature is attained, balance detector 8 willbe actuated and will send a signal to switch off key 10, said key beingthe control element of the temperature stabilizer. This actiondeenergizes thermistor 5, and there commences thermistor cooling. Aftera certain delay governed by self-actuating means 19, key will againclose the circuit. This sequence of operations is repeated continuouslyuntil the measuring period is commenced at a moment of feeding anexternal control signal via circuit 25 to keys 21 and 23.

Key 21 serves to switch resistor 18 in or out of the measuring bridgecircuit, which action alters the ratio of bridge arm resistances. Nextthere starts the transition period of heating thermistor 5 from thestabilization temperature to another temperature, whosemagnltudeldepends upon the ratio of resistances of the measuring bridgearms formed by thermistor 5 and resistors 2, 4, 16 and 17.

The process of heating is accompanied by the desorption of thepreviously absorbed gas mixture component, the time interval from themoment of switching on key 23 to the moment of switching off key 10 iscontrolled by meter 9. This sequence of gas analyzer operation havingbeen terminated, an external control signal fed to circuit 26 actuates-keys 20 and 24, and this action switches resistor 17 out of or in themeasuring bridge, so that there occurs a transition process ofafter-heating thermistor 5 to another temperature and an appropriatesignal is fed via key 24 to time interval meter 22, said transitionprocess being analogous to that described earlier.

In said gas analyzer modification, the operating mode can be illustratedby a temperature (T) vs. time (1) graph for thermistor 5 coated withsorbent 7 (FIG. 6). In the graph, To denotes the stabilizationtemperature of thermistor 5; T1 and T2 are the temperatures to which isheated thermistor in the course of two successive measuring steps; t1and t2 are the time intervals measured by meters 9 and 22, whcih makepossible the estimation of the concentration of gas components thatundergo desorption in appropriate temperature intervals.

In time intervals between measurements, a pulsating voltage normally fedto the measuring `bridge is supplied to integrating unit 27, whichgenerates a direct eurent output signal proportional to differencebetween the stabilization temperature of thermistor 5 and the sample gastemperature. Said output signal makes it possible to evaluate thetemperature of the gas being analyzed and to check whether the electriccircuits of the gas analyzers are intact.

The fourth modification of the gas analyzer (FIG. 4) operates in amanner similar to that of the third gas analyzer modiflication describedherein before, except for the fact that during time intervals thatprecede measurements the measuring bridge arm incorporates auxiliarythermistor 30 in place of thermistor 5, the resistance of thermistor 30being selected so as to balance the bridge at a pre-set stabilizationtemperature. Thermistor 30 serves to heat thermistor 5 and thesurrounding sample gas to said stabilization temperature. To carry outmeasurements, an external control signal is fed to circuit 32, therebysetting key 23 in the on position, while 4key 31 disconnects thermistor30 from the measuring bridge arm and incorporates thereinto thermistor 5in place of thermistor 30. The resistance of thermistor 5 is selected sothat at a new pre-set temperature the measuring bridge will be balanced,the duration of heating thermistor 5 in order to attain said temperatureproviding an output signal measured by time interval meter 9.

The fth modiiication of the present gas analyzer (FIG. 5) functionssimilarly to the fourth modification of the gas analyzer, except for thefact that feeding an external control signal to circuit 32, apart fromsubstituting thermistor 5 for auxiliary thermistor 12 in the measuringbridge arm, results simultaneously in connecting to the power supplycircuit second thermistor 13 and resistor 13, which, in conjunction withresistors 3 and 4, constitute the second measuring bridge.

As pointed out earlier in the second modification, thermistors 5 and 12are coated with diierent sorbents 7 and 14, respectively, and undergoheating during unequal time intervals. By using time interval meter 9both the duration of each thermistor, 5 and 12, heating and thedifference of these durations can be measured.

The implementation of the technique suggested herein in the gasanalyzers enables to obtain gas analyzers of simple design, smalldimensions and power consumption, and to adjust the gas analyzer formeasurements of various components by mere switching of the thermistor.

Moreover, the gas analyzers, according to the invention, provide thepossibility of measuring the temperature of the gas being analyzed andof checking continuously the circuitry.

What is claimed is:

1. A method of gas analysis, particularly of measuring the concentrationof moisture, which comprises absorbing the gas being analyzed by meansof sorbents, followed by heating at least one sorbent until it attains apre-set thermal state, which state characterizes the amount of the gasthus desorbed, e.g. to a temperature at which desorption is at amaximum, and measuring, during the process of heating, the period oftime required for the sorbent to attain said thermal state, said periodof time being indicative of the concentration of the absorbed gascomponent.

2. A gas analyzer for carrying out gas analyses, which comprises atleast one measuring bridge, a power source for energizing said measuringbridge; resistors, which form some of the arms of said measuring bridge;at least one thermistor placed in the gas being analyzed andconstituting, in conjunction with said resistors, all the arms of saidmeasuring bridge; a sorbent that coats said thermistor and absorbs a gasmixture component to be analyzed; time interval meter; a balancedetector incorporated into the measuring diagonal of said measuringbridge and intended to generate a signal which is fed to the input ofsaid time interval meter once said thermistor attains a pre-settemperature; a key incorporated into the other diagonal of saidmeasuring bridge and intended to switch on power supply from said powersource to said measuring bridge; to send the signal of said thermistorheating start to the input of said time interval meter.

3. A gas analyzer according to claim 2, wherein 8 said key comprises abalance detector-controlled control element of the temperaturestabilizer of said thermistor, provision being made for means ofthermistor temperature setting.

4. A gas analyzer according to claim 3, wherein in said key provision ismade for a delayed self-actuating means.

5. A gas analyzer according to claim 3, wherein said means oftemperature setting of said thermistor comprises one of said resistors,which form, in conjunction with said thermistor, said measuring bridge.

6. A gas analyzer according to claim 3, wherein said means oftemperaturesetting of said thermistor comprises an auxiliary thermistor, whichwarms up the sample gas in the Vicinity of said thermistor, coated withsaid sorbent, said auxiliary thermistor being switched into themeasuring bridge in place of said thermistor for a period of timepreceding the moment of determining the composition of the sample gas.

References Cited UNITED STATES PATENTS 2/1965 Crawford 73-29 4/ 1970Venezsky 73-19 U.S. Cl. X.R. 73-23

